For decades the standard coupling between a tractor and a semi-trailer has been a fifth wheel on the tractor, and a fifth wheel plate and king pin on the semi-trailer. The fifth wheel is supported on trunnions for pivotal movement about an axis parallel to the axis of the rear axle or axles of the tractor. The trunnions are rigidly secured to the bed of the tractor. In such an arrangement the semi-trailer king pin is pivotally supported within an opening in the fifth wheel, and relative rotational movement between the tractor and the semi-trailer is about the vertical axis of the king pin at the greased/lubricated bearing surface between the fifth wheel and the fifth wheel plate.
This same coupling arrangement has been and continues to be used as the coupling mechanism between semi-trailers and converter dollies. The converter dolly is, basically, a drawbar frame mounted on a wheeled axle (or axles) which is coupled to the King pin under the front end of a semi-trailer to convert it into a full trailer. Such full trailers are, via a conventional drawbar, coupled to the back of another semi-trailer to form doubles (two trailers connected in tandem) or, in some slates, triples (three trailers connected in tandem).
Since, the early 50's, the Holland Hitch Co., Holland, Mich. has offered a fifth wheel which is mounted on a rotary disc which, in turn, is secured to the tractor frame. This disc rotates about a vertical axis which is, approximately, 4 inches ahead of the vertical axis of the semi-trailer king pin. This rotating fifth wheel, sold under the Trailermaster trademark, also includes a pair of spring biased keys which lock into the slots provided in the fifth wheel plate of the semi-trailer, to prevent relative rotation between the fifth wheel and the fifth wheel plate about the king pin axis.
The Trailermaster hitch is always free to rotate about the vertical rotation axis of the disc on which it is mounted. To control jackknifing between the tractor and the attached semi-trailer, U.S. Pat. No. 2,692,145 to J. H. Hammond, Jr. et al. proposed applying a braking mechanism to a rotatable fifth wheel ("of the type known as the Holland-Apgar Safety Fifth wheel made by the Holland Hitch Co."; see column 2, lines 49-50). The mechanism includes a "brake band 23" which is used to lock the rotatable fifth wheel to "base plate 11".
In addition to J. H. Hammond et al., other rotating fifth wheels with anti-jackknifing controls have been proposed, including: U.S. Pat. No. 2,188,727 to H. A. Soulis; U.S. Pat. No. 2,667,364 to J. Colpo; U.S. Pat. No. 2,804,314 to L. E. Billingsley; U.S. Pat. No. 3,063,739 to P. M. Davies et al.; U.S. Pat. No. 3,328,051 to F. J. C. Hope et al.; U.S. Pat. No. 3,874,699 to P. Hays et al.; and U.S. Pat. No. 4,300,785 to B. J. Mettetal. In Billingsley an enlarged gear 48 is secured to the semi-trailer which mates with a pair of rotatable gears 58, 60 secured to the fifth wheel. Each rotatable gear is connected to a brake mechanism including hydraulic piston and cylinder arrangement 78. Billingsley states that: "it will be seen that by controlling the expansion and contraction of the hydraulic mechanism 78, the rotation of the gear 58 and 60 may be retarded or completely stopped, thereby restraining or stopping relative pivotal movement between the fifth wheel member 24 and the coupling plate 34 whereby relative pivotal movement between the trailer 12 and tractor 14 is eliminated or controlled, depending upon the force exerted on the control lever 86 or the brake pedal 98." See column 3, line 71 to column 4, line 5. In Davies, et al., the fifth wheel is supported on a rotatable subframe "so constructed and so arranged . . . to permit the trailer to swing about the axis of the trailer king pin or about a second vertical axis displaced forwardly thereof. See column 2, lines 31-39.
In addition to rotating fifth wheels with brake mechanisms between the tractor and the semitrailer, rotating fifth wheels with brake mechanisms on converter dollies have been disclosed in U.S. Pat. Nos. 3,556,560 and 4,898,399, both to C. R. Adams. A similar arrangement in which a steering brake is incorporated in a four wheeled or full trailer is disclosed in U.S. Pat. No. 2,838,323 to R. H. Coustillac. It is intended to prevent jackknifing of the trailer in a backing situation.
Despite all of the foregoing disclosures, to applicant's knowledge there is no commercially available tractor, full trailer or converter dolly which incorporates a rotating fifth wheel with an associated braking mechanism to control or prevent the rotation thereof. While the Trailermaster hitch has been available for, apparently, over 30 years it has not, to applicant's knowledge, seen much commercial utilization. Also, it is not supplied with any braking mechanism. While C. R. Adams and/or Aramar Inc. (the assignee of the U.S. Pat. No. 4,898,399 patent) built a prototype, there is no known commercialization of any of the features disclosed therein. Converter doilies have remained essentially enchanted for over 30 years.
The object of the present invention is to provide for converter dollies, permanently attached dollies and rotatable tractor fifth wheels which incorporate sate and reliable fifth wheel braking units that are electronically controlled; include, to the extent possible, off the shelf components (which here-to-fore have not been used in combination with each other); have a minimum number of moving parts; are easy to manufacture, use, and repair; and are designed to handle the loads and stresses which are typically encountered in the trucking industry.
It is a further object of the invention to provide a converter dolly in which, in relation to the front of the dolly, the axis of rotation of the fifth wheel comes first, followed by the axis of the semi-trailer king pin, followed by the axis of the axle. This arrangement has the advantage of forcing the trailer to follow the dolly in a straight line before full lock up of the fifth wheel on the dolly.
It is another object of the present invention to provide, in a converter dolly (or permanently attached trailer dolly, or rotatable tractor fifth wheels with a braking mechanism) a clutch/brake mechanism which has only one moving part, in which the force applied to the friction drum is applied uniformly around the entire circumference of the friction drum, and in which the force of engagement is selectively and easily controlled.
It is another object of the present invention to provide for electronic and pneumatic apparatus for selecting the force applied to the friction drum, to provide for various levels of force, for use in various driving conditions, both forward and reverse.
It is a further object of the present invention to provide an electronic control mechanism which relays the tractor driver's instruction to the rotatable fifth wheel clutch/brake mechanism, which measures the response of the clutch/brake mechanism and provides verification information back to the driver. Preferably the instructions and response are implemented through a single control wire.
It is a further object of the invention to, via a single wire (specifically the typically unused seventh wire in the standard 7-wire cable used in the trucking industry), send and receive signals between electronically controlled devices (such as the clutch/brake mechanism of the present invention) mounted on a dolly (or trailer or semi-trailer) and a microprocessor located in the tractor.